1. Field of the Invention
The present invention relates to a power supply circuit device for a high intensity discharge lamp lighting device to light a high intensity discharge lamp.
2. Description of the Prior Art
The power supply circuit device for the high intensity discharge lamp lighting device is used for lighting a high intensity discharge lamp such as a lamp for a projector. FIG. 4 shows a circuit diagram for a conventional high intensity discharge lamp lighting device using a high power-factor inverter. In FIG. 4, a power-frequency AC power is rectified to a direct current by a rectifier including diodes D101-D104, an inductor LF, and a condenser CF, and the output is applied to a booster chopper mode sine wave converter including a choke coil L101, a switching element SW1, a diode D105, and a condenser C. The booster chopper mode sine wave converter is connected to a full-bridge mode inverter INV as the load.
The booster chopper mode sine wave converter will briefly be explained.
In order to make the wave form of an input current Ii identical to that of the power-frequency supply voltage ei, first, a voltage ei' is detected by resisters R101, R102 to be fed to a multiplier MP1. This voltage is transferred to a current command reference Ii* having the same wave form as the voltage ei'. On the other hand, a current Ii' is detected by a resister R104 and a comparator COMP1 compares Ii' to Ii* to produce a PWM signal proportional to the difference between Ii* and Ii'. Driving a switching element SW1 of the sine-wave converter by this PWM signal achieves suppression of higher harmonics and higher power factor by the feed forward control. Further, in order to stabilize the output current of the inverter INV, a lamp current detecting resister R105 detects a lamp current IL. A variation .DELTA. IL of the lamp current IL is obtained by a constant-current circuit, and the multiplier MP1 makes a product by .DELTA. IL and ei' to produce the current command reference Ii*. And, a feedback circuit is configured, the amplitude of Ii* varies according to the variation of IL, i.e., .DELTA. IL, thereby IL is stabilized and at the same time the current waveform identical to ei' can be obtained.
Thus, since the average current by each switching is proportional to the input voltage, removing higher harmonics of the switching wave form by means of a low pass filter consisting of an inductor LF and a condenser CF makes the wave form of the input current analog to the input voltage with regard to one cycle of the AC line as shown in FIG. 5, and the power factor becomes almost 1. The booster chopper mode sine wave converter is connected to the full-bridge mode inverter INV as the load. TR1-TR4 are switching transistors configuring the inverter INV. The output of the inverter INV is connected to the secondary coil of a transformer T101 and a halide lamp L (HID, hereinafter) in series.
In order to light the HID lamp L, as the entire circuit shown in FIG. 4 is powered, a timer circuit TM is activated to feed a 100 Hz starting trigger pulse to a starting pulse generator PG. The starting pulse generator PG feeds a starting pulse for about five seconds, and the starting pulse is boosted to 3-5 KV by a transformer T101. Further, the timer circuit TM feeds an inverter starting signal to an oscillator OSC, thereby the oscillator OSC starts operation, whose output activates a drive circuit DCC; which in consequence activates the inverter INV.
As the inverter INV operates, the HID lamp L enters in a lighting state, transferring the state from a glow discharge to an arc discharge. In order to control the current running through the HID lamp L into a constant value, the inverter current, i.e., the lamp current is detected by the lamp current detecting resister R105, which is fed to a control IC. And, the control IC feeds a signal to a DRIVE CIRCUIT as the control input terminal of the booster chopper mode sine wave converter so as to suppress the lamp current if it goes high and to increase the lamp current if it goes low, thus controlling the inverter INV into a constant current. Namely, if the lamp current increases by any reason, the voltage across the lamp current detecting resistor R105 will increase. Therefore, the output voltage of the booster chopper mode sine wave converter decreases by the PWM operation of the booster chopper mode sine wave converter, which maintains the constant current operation.
The foregoing conventional inverter is well known that it has restrictions for a smaller size. When lighting the halide lamp at a high frequency, the lamp current will fade out to lead the lamp to an unstable operation due to the acoustic resonance effect if the inverter INV oscillating frequency is lass than 300 KHz. Therefore, the switching frequency is selected to less than some 100 Hz not inducing the acoustic resonance. In the full-bridge mode inverter, generally, the switching frequency is apt to be less than 400 Hz due to the restriction of the switching elements such as the switching speed, thereby the transformer T1 is difficult to be made smaller.
The control circuit and the drive circuit of the full-bridge mode inverter are complicated and costly.